This invention relates generally to a soldering apparatus and, more specifically, to an apparatus for soldering printed circuit boards traveling along a predetermined path with the use of a combination of a molten solder wave and vapors of a heat transfer liquid.
There is known a vapor phase soldering method in which the objects to be soldered are heated to a temperature appropriate for the soldering operation by condensing thereon hot vapors of a heat transfer liquid. U.S. Pat. No. 3,866,307 discloses a vapor phase soldering apparatus employing a solder wave formed within a chamber filled with saturated vapors of a heat transfer liquid. With such an apparatus in which the vaporization of the heat transfer liquid is effected by a heater disposed in the chamber, it is difficult to control the temperature of the solder wave and the generation of the vapors of the heat transfer liquid. Further, the conventional apparatus requires frequent exchange or make up of the heat transfer liquid due to the inclusion of dusts or the like impurities which cause the deterioration of the heat transfer liquid.
The present invention has been made from the consideration of the above-described problems in the conventional soldering apparatus. In accordance with the present invention there is provided an apparatus for soldering printed circuit boards, comprising:
a first closed vessel;
a second closed vessel for containing a heat transfer liquid having heating means for vaporizing the heat transfer liquid within said second vessel;
first conduit means extending between said first and second vessels and provided with a first pump adapted to feed vapors of the heat transfer liquid in said second vessel to said first vessel through said first conduit means;
second conduit means extending between said first and second vessels and provided with a second pump to recycle heat transfer liquid collected in said first vessel to said second vessel;
entrance and exit ports provided in the first vessel;
conveying means adapted to support printed circuit boards thereon and to convey same along a predetermined path extending through said first vessel;
cooling means provided adjacent to said entrance and exit ports for condensing vapors of the heat transfer liquid and preventing same from escaping through said entrance and exit ports from said first vessel; and
means for forming a solder wave within said first vessel;
whereby the printed circuit boards supported on said conveying means are introduced through said entrance ports into said first vessel, contacted with the solder wave and discharged through said exit port from said first vessel, with the vapors of the heat transfer liquid being condensed upon contact with the printed circuit boards and collected in said first vessel.
The present invention will now be described in more detail with reference to the accompanying drawings in which: